Export from producers platform fail for 1 product with empty imported_date field

[stephanegigandet]

Reported by @manon-corneille for product https://fr.openfoodfacts.org/produit/3038359003394/lustucru-risotto-facile-5 on org-lustucru-frais

The import on the public platform fails, and in the logs the last line is:

[4933] ProductOpener/Import.pm 947 ProductOpener.Import {} product already exists {code => "3038359003394",product_id => "3038359003394"}

Adding some debug logs and running the minion_producers.pl directly (after stopping the minion service)
/srv/off/scripts/minion_producers.pl minion worker -m production -q openfoodfacts.org

The issue seems to be a parse time on an empty string:
[4934] ProductOpener/Import.pm 967 ProductOpener.Import {} xyz - before defined imported_date {code => "3038359003394",existing_date => "2021-03-10T11:28:41+01:00",imported_date => ""}
[4934] ProductOpener/Import.pm 971 ProductOpener.Import {} xyz - before parse time {code => "3038359003394"}